The latest geopotential model, EGM96, was employed to compute the free-air gravity anomaly, geoidal separation, the average density anomalies of the crust and the uppermost mantle, and the distribution pattern of the viscous stress exerted by mantle convection over Xinjiang and its neighboring areas. Based on these results and other data, we try to interpret the geodynamical features of the Tianshan orogen. Our research suggests that the Tianshan orogen is in a tectonic setting of compressive settling, driven by mantle convection. Under the effect of the compressive stress field, asymmetric in north-south direction, the Tianshan orogen upheaved quickly. The center of compressive stress field is in the south of the Tianshan, and the characteristic of stress field is favorable for the view point that the Tarim plat subducts beneath the Tianshan. The southern margin of the Juggar basin and the northern margin of the Tarim basin are two areas where the crust is of mass deficiency. We attribute the mass deficiency to the fact that the crust, in both the north and the south of the Tianshan is bent downwards under the compressive stress. Our research also indicates that the density distribution patterns in the deep of the eastern Tianshan are different from those in the middle and western Tianshan. It may be explained as the results from the east-west oriented distinction of the mantle convection.